This invention relates to a multilayer heat activated adhesive film with improved control of its peel properties. The invention also relates to cable jacketing or shielding structures that use such films.
It is well known to use adhesive films in cable shielding structures having internal metal layers requiring adhesion to outer coverings of a plastic protective layer; such as in coaxial, fiber optic, electrical power and other communications cables.
In general such films are intended to tightly adhere the outer plastic jacket or coating to the inner metallic surface or layer. In the general process for preparing a shielding laminate structure and use in a coated or jacketed cable, an adhesive film is first laminated on one side of thin gauge metal, e.g., steel, by: (a) preheating the metal, (b) contacting the film to the metal, (c) further heating to increase the bond strength, (d) cooling and (e) winding onto a roll. This film-coated metal sheet or strip is sometimes referred to as “shielding tape”. This laminate, in appropriate widths, is subsequently formed into tubes, often corrugated tubes, which have conductive member(s), e.g., wiring or fiber optic cables, in the center of the tubes with the laminated adhesive film on the outside of the tube. Then, a thermoplastic polymer jacketing or coating (often HDPE) is extruded over the tubing and the heat from the polymer creates a bond between the jacketing and the film. The adhesive film inter-layer bonds and bonds to the metal and outer jacketing are desired to withstand delamination under conditions of normal production, installation and use but also allow the outer plastic jacket material to be easily and consistently peeled back from the central metal encased conductive member(s), and removed to facilitate the grounding, splicing and other procedures that may need to access the metallic layer and/or the central conductive member(s). The peeling and removal is preferably performed or performable by hand or arm force, which corresponds to having a peel strength or bond strength on the order of less than about. When the outer plastic jacket material is peeled back away from the metal, the film needs to be sufficiently adhered to the metal and structured such that, interlayer delamination during outer jacket removal leaves a sufficiently thick, residual protective coating tightly adhered to the metal at all times for protection against corrosion following the removal of the jacket.
U.S. Pat. No. 4,125,739 discloses a two layer film or a three layer film where an adhesive layer bonds strongly to the metal sheathing. In the two layer film, the other layer has a strippable bond to the cable jacketing. For the 3 layer film, the outside layer bonds strongly to the cable jacketing material, and the core layer is strippable from either adhesive layer.
U.S. Pat. No. 4,767,894 A discloses an annular cable coating having at least three extruded layers around a conductor. The intermediate layer between first and second layers is strippably bonded to the first layer and fully bonded to the second layer such that the second layer together with substantially all of the intermediate layer is readily strippable from the first layer. In particular, it relates to an insulated electrical cable in which such laminate construction coextruded substantially coaxially around a core conductor and not provided in the form a film.